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Author Topic: JBL MP418SP popping sound at about 90hz  (Read 6653 times)

Jared Bartimus

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JBL MP418SP popping sound at about 90hz
« on: April 12, 2011, 01:58:50 pm »

A campus ministry program I help out purchased a used MP418SP a few months back and we have been having problems with popping ever since.  When the system is run anywhere near its limit we get a popping sound in the 80-100hz range.  Before I had assumed we were sending out too much in the lower ranges and bottoming out the driver.

The frequency was determined by playing the 80hz warble from the Bink Audio Test CD and then using individual test tones to narrow it down.  Low cut on the channel strip was turned off and the main eq's had, I believe, a 40hz low cut engaged.  Every time the tone would hit the middle of the range the sub started popping.  EQ was set flat for everything below about 120hz and there were no significant changes above that point.

It started popping both when pushed fairly hard at that frequency and when I was moving the fader relatively quickly at a lower level.  I don't know if that part was an issue with the sound board or something to do with the sub.

Is the original assumption that we are doing something wrong and causing it to bottom out probably correct or was the driver maybe somehow already damaged when we got it?  It doesn't seem right that the sub has extreme difficulty keeping up with a pair of JRX115's that are being powered to the same combined wattage.  I know we aren't going to be getting a strong hit from the kick drum with only a single 18" sub in a room as big as we are in but it had trouble getting over stage volume even with just two people singing and an acoustic guitar.
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Bennett Prescott

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Re: JBL MP418SP popping sound at about 90hz
« Reply #1 on: April 12, 2011, 02:56:50 pm »

It sounds like over excursion, but if it's happening with quick fader moves at low levels (or with things that should not be creating sub bass, like an acoustic act) then the problem may lie elsewhere. Check your cable connections, maybe one of them has gotten a little corroded.
« Last Edit: April 12, 2011, 02:58:44 pm by Bennett Prescott »
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Jared Bartimus

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Re: JBL MP418SP popping sound at about 90hz
« Reply #2 on: April 12, 2011, 03:42:03 pm »

I thought it was overexcursion myself, but shouldn't that get worse at lower frequencies? At 110hz it is fine and at 70hz it is fine but at 80-100hz it isn't.  If I remember correctly pretty much every connector in the sytem has been checked within the past 6-9 months due to other issues we had been having. 
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Tim McCulloch

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Re: JBL MP418SP popping sound at about 90hz
« Reply #3 on: April 12, 2011, 05:46:09 pm »

I thought it was overexcursion myself, but shouldn't that get worse at lower frequencies? At 110hz it is fine and at 70hz it is fine but at 80-100hz it isn't.  If I remember correctly pretty much every connector in the sytem has been checked within the past 6-9 months due to other issues we had been having.

Can you find another MP418 to compare with?  I don't think it's the loudspeaker itself...

If it were, it would be more likely to bottom out at lower frequencies (particularly at/below the box tuning freq) and that would be at levels below maximum power.

I suspect what you're hearing is a cabinet issue... a broken glue joint, failed fastener, etc that resonates at 70Hz.... or there is something loose in the box that starts moving when the box resonates at 70Hz.

Perhaps Art Welter can share his considerable experience with such things....

Have fun, good luck.

Tim Mc
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Jared Bartimus

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Re: JBL MP418SP popping sound at about 90hz
« Reply #4 on: April 12, 2011, 07:22:15 pm »

Can you find another MP418 to compare with?  I don't think it's the loudspeaker itself...

If it were, it would be more likely to bottom out at lower frequencies (particularly at/below the box tuning freq) and that would be at levels below maximum power.

I suspect what you're hearing is a cabinet issue... a broken glue joint, failed fastener, etc that resonates at 70Hz.... or there is something loose in the box that starts moving when the box resonates at 70Hz.

Perhaps Art Welter can share his considerable experience with such things....

Have fun, good luck.

Tim Mc

Thanks for the suggestions so far.  It sounds like it is coming from the driver itself but it could still be an issue in the cabinet near the driver. 
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Tim Weaver

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Re: JBL MP418SP popping sound at about 90hz
« Reply #5 on: April 13, 2011, 12:08:22 pm »

It very well could be overexcursion. This is a ported cabinet. The tuning frequency would be somewhere in the 35-40 hz range I'm guessing. The excursion is controlled at that frequency so the woofer hardly moves at all. Above and below the tuning frequency is a different story all together. I would imagine that the speaker is bottoming out around 90 because that would be the highest point in it's operating range before the low pass filter takes over (I'm guessing around 125 ish?). Also the port tuning keeps excursion under control down to the 40 hz range and the HP on the graph will prevent problems below tuning.

Therefor it seems that around 80-90 hz would be the only place where excursion is relatively left unchecked on this particular system. It wouldn't be hard to drive it into overexcursion.

Buy more subs if you want it that loud.
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Jared Bartimus

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Re: JBL MP418SP popping sound at about 90hz
« Reply #6 on: April 13, 2011, 12:42:19 pm »

It very well could be overexcursion. This is a ported cabinet. The tuning frequency would be somewhere in the 35-40 hz range I'm guessing. The excursion is controlled at that frequency so the woofer hardly moves at all. Above and below the tuning frequency is a different story all together. I would imagine that the speaker is bottoming out around 90 because that would be the highest point in it's operating range before the low pass filter takes over (I'm guessing around 125 ish?). Also the port tuning keeps excursion under control down to the 40 hz range and the HP on the graph will prevent problems below tuning.

Therefor it seems that around 80-90 hz would be the only place where excursion is relatively left unchecked on this particular system. It wouldn't be hard to drive it into overexcursion.

Buy more subs if you want it that loud.

How much does the frequency response graph relate to the actual driver excursion? I am bad at reading these graphs but it looks like 90hz is actually almost the lowest output before the crossover kicks in.

http://www.jblpro.com/mpro/PDF/MP418SP.pdf

I do agree that more subs are needed, but until that becomes a possibility I wanted to make sure we weren't just fighting a lost cause to do an already damaged driver/cabinet.
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Micky Basiliere

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Re: JBL MP418SP popping sound at about 90hz
« Reply #7 on: April 13, 2011, 01:03:08 pm »


Does NOT sound like "over excusion" i have 4 of these cabs,and they can be pushed very hard! If you where pushing these cabs hard enouph to "pop" the drivers the amp would go into protect mode before damage occured. Look at the clip indicators on the back of the cab to see if they're lighting up when its being pushed...if they are,that's you problem! if not, the problem is somewhere else??? just sayin'...

A campus ministry program I help out purchased a used MP418SP a few months back and we have been having problems with popping ever since.  When the system is run anywhere near its limit we get a popping sound in the 80-100hz range.  Before I had assumed we were sending out too much in the lower ranges and bottoming out the driver.

The frequency was determined by playing the 80hz warble from the Bink Audio Test CD and then using individual test tones to narrow it down.  Low cut on the channel strip was turned off and the main eq's had, I believe, a 40hz low cut engaged.  Every time the tone would hit the middle of the range the sub started popping.  EQ was set flat for everything below about 120hz and there were no significant changes above that point.

It started popping both when pushed fairly hard at that frequency and when I was moving the fader relatively quickly at a lower level.  I don't know if that part was an issue with the sound board or something to do with the sub.

Is the original assumption that we are doing something wrong and causing it to bottom out probably correct or was the driver maybe somehow already damaged when we got it?  It doesn't seem right that the sub has extreme difficulty keeping up with a pair of JRX115's that are being powered to the same combined wattage.  I know we aren't going to be getting a strong hit from the kick drum with only a single 18" sub in a room as big as we are in but it had trouble getting over stage volume even with just two people singing and an acoustic guitar.
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Jared Bartimus

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Re: JBL MP418SP popping sound at about 90hz
« Reply #8 on: April 13, 2011, 01:25:13 pm »

Does NOT sound like "over excusion" i have 4 of these cabs,and they can be pushed very hard! If you where pushing these cabs hard enouph to "pop" the drivers the amp would go into protect mode before damage occured. Look at the clip indicators on the back of the cab to see if they're lighting up when its being pushed...if they are,that's you problem! if not, the problem is somewhere else??? just sayin'...

It is right near the edge of clipping but it does it without the clip lights coming on.  In theory that cabinet is rated for about 2400 peak and the internal amp is only putting out about 600W peak.  I believe the only design difference is a slightly larger cabinet to make up the room taken by the amp.  I am sure it is still possible to bottom out the driver with the right frequency though.
« Last Edit: April 13, 2011, 01:39:20 pm by Jared Bartimus »
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Gus Housen

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Re: JBL MP418SP popping sound at about 90hz
« Reply #9 on: April 13, 2011, 01:42:46 pm »


The fact that it is recreatable with low level rapid fader movement suggests it could be another issue. You may even try to borrow or rent a nother cabinet of the same. If it reproduces in both you probably have some other issue, If not its possible you got a bad one "out of the box".
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Re: JBL MP418SP popping sound at about 90hz
« Reply #9 on: April 13, 2011, 01:42:46 pm »


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